如果助动词或Be动词后面是表示单数的名词或第三人称单数,就用does或is,比如说,he; she; my dad; a book之类的,如果是名词复数或第一二人称就用 do 或 are,比如说 I; we ; they ; you ; students(名词复数);many books ;等等
例句:are there more than 30 students in your class?你们班有超过30个学生吗?
are you student?你是学生吗?
Do they finish homework?他们完成作业了吗?
is she your friend?她是你朋友吗?
does your teacher tell you that?你的老师告诉你那件事了吗?
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